Doctors, nurses, parents, and other care providers all need to be able to rapidly and accurately measure a person's body temperature. To find out whether a person is sick, the first thing a care provider usually does is take the person's temperature. Someone running a fever is likely to have an infection. A doctor or nurse can tell a lot about how a patient is doing by monitoring the patient's temperature over time and noting how it has changed.
There are three kinds of thermometers in wide use today:
glass thermometers, PA1 "electronic" thermometers, and PA1 ear ("tympanic") thermometers. PA1 The measuring time is very rapid--usually less than two seconds. PA1 The eardrum is at or near the body's core temperature, providing the most accurate location for non-invasive temperature measurement. PA1 Because the ear is a dry orifice, cross-contamination is not much of an issue--and individual, disposable probe covers further reduce the already low cross-contamination risks. PA1 The theoretical accuracy of the measurement is very high (for example, on the order of one tenth of one degree). PA1 Because of the short measurement time and the use of either ear as the measuring point, it is possible to rapidly measure the temperature of children, invalids and sleeping patients--and in other situations where it is difficult to get a patient to sit still for thirty seconds with a probe under their tongue. PA1 Highly accurate and sensitive; capable of achieving 0.1 degree Fahrenheit resolution. PA1 Cost-effective and easy to use. PA1 Measuring unit probe end is specially adapted to use foam probe covers of the type disclosed in U.S. patent application Ser. No. 08/867,838 of Cheslock et al entitled "Tympanic Thermometer Probe Covers" (attorney docket no. 2204-7) filed Jun. 3, 1997. PA1 Different, interchangeable probe end tips can be used to accommodate various types of probe covers including a foam design, a rigid polystyrene design and a thin film design. PA1 Modularized temperature-sensing head and electronic control package streamlines production and testing while providing for various packaging configurations and deployment methods. PA1 Meets or exceeds all current ASTM requirements. PA1 The modular sensing probe has unique thermal characteristics, and is capable of operating over a wide dynamic temperature range with accuracy down to a fraction of a degree, in both Fahrenheit and Celsius. PA1 The modular sensing probe provides excellent thermal characterization while accommodating versatile hardware support and generous software headroom. PA1 The modular sensing probe can provide a high degree of accuracy and compatibility with a range of different host platforms and configurations. PA1 Low power requirements. PA1 Sensor module is programmable; base unit or other host can download configuration information to sensor module. PA1 The self-contained, removable, replaceable sensor module and memory module allow for simple field replacement without returning the entire thermometer to the manufacturer for reconditioning. PA1 A conventional 4-conductor modular coiled telephone handset cord can be used to communicate signals and power between the base unit and the measuring unit. PA1 All analog circuitry is mounted on a compact circuit board within the sensor module. The single compact circuit board can contain all power supply and analog circuitry (including A/D converter and associated digital signal processor) required to make thermopile and thermistor fully functional. PA1 Epoxy material can be used to pot all components of a sensor module. For example, the analog circuitry and thermopile can be bonded permanently with thermally-conductive epoxy to a screw-machined, cylindrical housing. The epoxy minimizes any chance of mechanical damage to the thermopile and electronic components--and the entire sensor module is water-tight, water-proof and shock-resistant. PA1 Analog components, including the thermopile, can be potted together in thermally conductive epoxy to equalize temperatures between components--constraining all electrical thermal drift offsets isothermally and providing an isothermal relationship of the thermopile cold junction and the analog processing circuitry. PA1 All communications to and from the sensor module are in the form of digital signals. All interfacing between the sensor module and the rest of the system is at a TTL digital level. In one example embodiment, a single (e.g., 4-pin or 12-pin) connector can be used as the only normally used interface to the sensor module--providing an unregulated DC supply and a digital interface for thermometry operation. PA1 The sensor module casing can be made of a conductive material such as machined aluminum--providing high electrostatic field and RF isolation and good heat transfer. The analog circuitry and the screw-machined housing are electrically grounded externally to the sensor module. This configuration allows the sensor module screw-machined housing to act as an electrostatic and Faraday shield, increasing the signal-to-noise ratio (e.g., to -160 dB for 50-60 Hz), and offering general isolation from radiated noise sources across a wide bandwidth. The shield also reduces spurious RF emissions such as radiated broadband noise--ensuring compliance with FCC Part 15 specifications. PA1 The thermistor can be embedded within the thermopile can to simplify construction and ensure higher reliability and close thermal coupling. PA1 An operational amplifier within the sensor module amplifies the thermopile output with a gain optimized to ensure that at conventional ambient hospital temperatures, there is adequate separation between two adjacent 0.1 degree A/D conversion points. PA1 The sensor module may include an A/D converter and an on-board microcontroller--providing programmability and flexibility. PA1 An A/D converter integral within the sensor module housing may employ a scaleable and programmable analog gain amplifier and low pass digital filter--allowing for characteristic responsivity differentials between thermopiles so that the sensor modules can be made identically. The lowpass filter decreases the overall noise figure while providing high noise rejection (e.g., rejection of noise in the 50-60 Hz range). PA1 The tip of the sensor module (where the removable probe covers attach) can be made of a thermally non-conductive material--reducing adverse potential accuracy degradation due to "drawdown." A non-conductive thermal barrier reduces any tendency of the sensor module to draw heat off of the ear canal, and further coupled with the preferred thermally insulative foam-based probe cover design, better permits the clinician to secure same-ear repeatability PA1 The tip of the sensor module, the lens, and the optical waveguide are removable and replaceable parts. This allows for the easy and simple replacement of the most vulnerable mechanical components. PA1 The cylindrical sensor module housing is a screw-machined part with no moving assemblies. This design negates the need for any kind of mold for manufacturing while permitting multiple vendor sources. It dramatically reduces the initial manufacturing investments while keeping production-quantity costs low. It also significantly increases the total MTBF (mean time between failures) of the assembly. PA1 In one embodiment, the sensor module includes waveguide closed by a polyethylene, silicon or germanium lens. The lens protects against accuracy degradation due to dirt and grime. The waveguide can easily be removed and replaced in the event that the lens becomes scratched. PA1 The machined sensor module and its associated analog circuit design easily allows for multiple-sourced thermopiles without tooling or design changes being made. This takes advantage of the subtle size and responsivity differences seen from thermopile manufacturer to manufacturer, without compromising performance. It also negates the cost of carrying different types of physical inventory in the event that an alternate thermopile is required, as well as the cost of any additional design burden. PA1 The sensor module can, in one embodiment, provide an analog input for resolving black body target reference temperature during calibration. This feature serves at least two purposes: it allows an external voltage source to be used to set the system gain and calibration ranges, and it simplifies the manufacturing support tooling used to calibrate sensor modules. PA1 The sensor module can withstand rough treatment and dropping without significant damage. The overall design is virtually impervious to damage when physically mounted to a thermometer chassis so that the connector pins are not exposed. Damage to the waveguide lens resulting from dropping the unit in such a way that the lens absorbs most or all of the impact of a drop from a significant height can be cured by replacing the waveguide and recalibrating. PA1 The sensor module can be commanded to perform multiple A/D conversions, separated in time, to separate signal from noise. In one embodiment, the A/D converter for each displayed temperature, samples the thermistor output, then samples the thermopile output multiple times, then again samples the thermistor output. Sample averaging can be used to improve accuracy and noise rejection. PA1 Since positioning technique is an important part of temperature repeatability and the clinician may know best when all the criteria have been met for proper placement, the measuring unit may include a temperature button that the clinician manually depresses to trigger a temperature reading. PA1 In another embodiment or mode of operation, the thermometer can automatically initiate a temperature measurement when it senses that the patient's ear canal has been sealed, and the proper pressure applied. PA1 Probe cover sensing mechanism prevents cross-contamination from an unprotected probe tip being inserted into the ear, or by a used probe cover being inserted into the patient's ear. PA1 Magnetic (e.g., linear Hall Effect) sensors within the sensing probe module can be used to detect push button depression and/or probe cover positioning--allowing the sensing probe module to house all measuring unit electronics, and eliminating all wires or interconnects from the sensing probe module. PA1 Possible to sense when the probe cover has sealed the patient's ear canal, and to automatically perform and/or disable temperature measurement until sealing has occurred (thus achieving a high degree of repeatability and encouraging the clinician to use an improved technique). PA1 Magnetic (e.g., linear Hall Effect) sensors within the sensing probe module can be used to sense when the probe cover has sealed the patient's ear canal by sensing over-travel and force exerted by the patient's ear onto the sensing probe module. One example senses force by allowing the probe module to be moveable with respect to its outer case, and spring biasing the probe module toward a forward position. A Hall Effect sensor can determine the amount of force being applied to the probe module by sensing its position--which has a predetermined relationship to the amount of force acting against the spring bias. PA1 Over-travel and force-sensing can be used to achieve a high degree of repeatability by automatically activating a temperature measurement and/or disabling temperature measurement until sealing has occurred (thus effecting improved technique). PA1 Probe module can be linked to a "personality" or memory module for simple and fast field replacement and/or repair. PA1 All tasking for probe cover position sensing, push button activation, A/D conversion, sampling and averaging and other functions can be performed within the sensing module. PA1 The microcontroller within the sensing probe module can be programmed to determine quiescent state and change of state of the Hall Effect sensor outputs. For example the microcontroller can look for an output change greater than a threshold to determine if a button has been pushed or a probe cover position-indicating magnet has been moved into a predetermined position. PA1 The probe cover ejection mechanism carriage can be spring loaded and movable, so a magnet that it carries moves away from an associated magnetic sensor when the probe is pressed into the outer ear. This allows the microcontroller to detect when the probe has been pushed into the outer ear. The system can be designed to remind the clinician to install a new probe cover before taking a temperature. PA1 Alternate unitary system embodiment can provide all necessary functions and capabilities within a single handheld, portable unit that also includes a unique probe cover ejection mechanism and a removable probe cover dispenser.
Glass thermometers are very inexpensive, very small and easy to store, and don't require batteries or other special supplies. For this reason, glass thermometers are probably the most widely used temperature measuring device in the home. However, glass thermometers have the disadvantage that they are very slow in making measurements--they typically require several minutes to reach body temperature. This is uncomfortable for the patient, and may be very troublesome when it is necessary to take the temperature of a small child or an invalid. In addition, glass thermometers are typically accurate only to within a degree, may be susceptible to errors in placement, and can be broken easily.
Because of these disadvantages, most hospitals and doctors' offices now use instruments commonly known as "electronic" thermometers. Most of us have had our temperature taken by an electronic thermometer at one time or another. The electronic thermometer includes a portable, hand-held battery powered unit with a display, and a separate probe. A wire usually connects the probe to the hand-held unit. The probe is long and thin, and has the same general shape as a glass thermometer. To use this kind of electronic thermometer, a nurse first covers the probe with a long thin disposable plastic probe cover that completely covers the probe. The disposable probe cover helps prevent the spread of disease by avoiding direct contact between the reusable probe and the germs in the patient's mouth. The nurse then puts the end of the probe under the patient's tongue. An electronic temperature sensor within the probe electrically senses the patient's temperature, and sends a signal to a microcomputer in the hand-held unit. The hand-held unit usually beeps when the temperature measurement is finished, and displays the patient's temperature on the display. The nurse can then remove the probe from the patient's mouth, strip the probe cover off the probe, and throw away the used disposable probe cover.
This type of electronic thermometer has achieved wide acceptance in hospitals because it is reasonably accurate, can be used with familiar placement techniques, and is (because of its disposable, replaceable probe covers) easily reusable for a number of different patients. Although the electronic hand-held unit is itself more expensive than most households are willing to pay, the overall cost of using this kind of electronic thermometer is relatively low because the disposable probe covers are inexpensive (two to three cents per cover, for example) and a single hand-held electronic unit may last for years and can be used to take the temperatures of many thousands of patients.
Electronic thermometers offer speed, ease of reading, and accuracy improvements over glass thermometers, and also eliminate the possibility of mercury poisoning. Although such electronic thermometers have achieved a fair degree of success, they have certain significant disadvantages. For example, they need to be constantly calibrated, are relatively easily broken, and often require a relatively long time (thirty seconds or more in many cases) to make an accurate measurement. There are also problems with taking a temperature from the patient's mouth due to breathing, keeping the thermometer under the patient's tongue, etc. Cross-contamination of infectious diseases is also a concern because the mouth is a "wet orifice."
More recently, a new kind of electronic thermometer has appeared on the market. This new kind of thermometer works by measuring the temperature of your eardrum. Since the eardrum is also known as the "tympanic membrane," these thermometers are sometimes called "tympanic thermometers."
Why the eardrum? The carotid artery that supplies blood to the hypothalamus--the body's temperature control center--passes through the eardrum. For this reason, the temperature of your eardrum corresponds very closely to the core temperature of your body. Although doctors and scientists have known this fact for many years, only since the mid-1980's have commercial devices been available to measure eardrum temperature in a clinical setting.
Ear or "tympanic" thermometers work by receiving and analyzing the radiant heat ("infrared") energy coming from the eardrum. Just as you can feel the heat when you hold your hands up in front of a warm fire, a tympanic thermometer can detect eardrum temperature without having to actually touch the eardrum by receiving the radiant heat energy coming from the eardrum.
Commercially available tympanic thermometers consist of a portable, hand-held battery powered main unit providing electronics, a display and a probe containing a special type of heat sensor such as a "thermopile" or a pyroelectric heat sensor. This special heat sensor is especially sensitive to the eardrum's radiant heat energy. Microelectronics can determine eardrum temperature from the electrical signals provided by the special heat sensor. The thermopile's sensing probe is typically an integral part of the tympanic thermometer's main unit--reducing the potential for breakage of the sensor assembly and (at least potentially) increasing reliability and accuracy.
To use the ear thermometer, a nurse or other care provider inserts a disposable probe cover onto the instrument's sensing probe. Once the disposable probe cover is in place, the nurse or other caregiver inserts the covered sensing probe into the patient's outer ear and then presses a button to command the instrument to make a measurement. The measurement time is usually very rapid--on the order of two seconds or less. The patient's temperature instantly shows on the instrument's display. The instrument may then be removed from the patient's ear, and the disposable cover can be stripped off the instrument and discarded.
Ear thermometry has advantages over other temperature measuring techniques. For example:
Despite these many clear advantages, ear thermometry has not yet achieved wide success in the medical marketplace. Even though many hospitals are believers in the concept of ear thermometry, the hospital market overall has converted less than twenty-five per cent of its temperature measurements to ear thermometry--and the hospitals that have converted are often displeased with their choice.
The main reason for past failures is that existing ear thermometer/probe cover combinations do not provide the high, repeatable accuracy required in a demanding hospital environment. Nurses are often unable to duplicate ear thermometer readings. If you try to measure the same person's temperature twice with existing commercial ear thermometer/probe cover combinations, you may get two very different readings. Since accurate, repeatable, temperature measurements are important or even critical to medical diagnosis and treatment (for example, to detect a 101.5.degree. F. hospital fever threshold or to establish a temperature pattern over time), it is important for temperature measurements to be as accurate and repeatable as possible.
The sensing probe used to sense the infrared radiation emitted by the eardrum plays an important role in the overall accuracy, repeatability and usability of the tympanic thermometer. For example, the sensing probe needs to be rugged and robust to withstand dropping and other rough treatment it may be subjected to in hospitals and other clinical setting. The sensing probe must also be sensitive to the low level of infrared energy emitted by an eardrum while providing a high degree of accuracy, repeatability and noise immunity. Much work has been done in the past to improve the reliability and accuracy of tympanic thermometer measuring systems. Several units currently on the market comply with the current industry standards. See, for example, "Standard Specification For Electronic Thermometer For Intermittent Determination of Patient Temperature" Designation E 1112--86 (Reapproved 1991) published by the American Society For Testing and Materials ("ASTM"); and the more recent draft proposed "Standard Specification for Infrared Thermometers For Intermittent Determination of Patient Temperature" (ASTM EXXXX-97, May 9, 1997), which specifications are incorporated by reference into this patent specification). However, further improvements are possible.
For example, several past designs incorporate the sensing probe as an integral part of the overall tympanic thermometer's structure. In one past example approach, the thermopile heat sensor is mounted on the same main circuit board that supports electronics used to measure and display temperature. One problem with this prior approach is that it can be difficult to repair or replace the sensing structure if anything goes wrong in the field. Thermometer head failure accounts for a large percentage of all tympanic thermometers being removed from service, so this integral design approach leads to inefficiencies in terms of long term product maintenance, repair and replacement. There are numerous other problems with prior tympanic thermometers that need to be solved.
The present invention solves many of these problems by providing a portable, self-contained tympanic temperature sensing system having many improvements in accuracy, repeatability, and reliability.
In accordance with one aspect provided by the present invention, an ear thermometer comprises a housing and a probe disposed within the housing. The probe is displaceable between first and second positions relative to the housing. A Hall Effect sensor disposed on at least one of the housing and the probe measures the displacement of the probe relative to the housing.
In accordance with a further aspect of the invention, the probe is biased to a forward position. In use, the probe is inserted into a patient's outer ear and the clinician applies pressure to seal the outer ear canal with the probe (and associated disposable probe cover if desired). This applied pressure forces the probe to move against the bias, rearwardly from its forward position. By measuring rearward probe displacement against this bias, the Hall Effect sensor can measures the amount of force the clinician is exerting to press the probe into the patient's outer ear. The thermometer can perform a predetermined action (e.g., automatically take a temperature) when the measured pressure exceeds a certain threshold (thus indicating that the ear canal has been sealed).
In accordance with a further aspect provided by the invention, an ear thermometer comprises an infrared sensor having a cold junction, and analog processing circuitry electrically coupled to the infrared sensor. Thermally conductive material bonded to the infrared sensor cold junction and the analog processing circuitry maintains the infrared sensor cold junction and the analog processing circuitry at substantially the same temperature.
In accordance with a still further aspect of the present invention, an ear thermometer modular sensing probe comprises a thermally and electrically conductive tubular body defining a hollow cavity therein. A miniature circuit board is disposed within the hollow cavity. The miniature circuit board has at least an infrared sensor and a temperature sensor disposed thereon. The infrared sensor having a cold junction, and the temperature sensor measures the temperature of the infrared sensor cold junction. The body also shields the miniature circuit board from electrostatic and RF fields, while virtually eliminating RFI emissions.
In accordance with a further aspect provided in accordance with the present invention, the tubular body is non-magnetic, and at least one Hall Effect sensor is disposed on the miniature circuit board. The Hall Effect sensor measures the position of at least one magnet moveable relative to the tubular body.
In accordance with a still further aspect provided by the present invention, an ear thermometer comprises a modular sensing probe including a probe casing defining a cavity therein, and electronics disposed within the cavity, the electronics including at least an infrared sensor and a temperature sensor, the infrared sensor having a cold junction, the temperature sensor measuring the temperature of the infrared sensor cold junction. A base unit is electrically coupled to the modular sensing probe, the base unit including at least one pluggable memory device. The base unit can be interchangeably used with any of plural modular sensing probes upon installation into the base unit of a pluggable memory device containing information specific to the modular sensing probe.
In accordance with a still further aspect of the present invention, an ear thermometer kit includes a sensor module comprising an infrared sensor having a cold junction, a tip mounting structure optically coupled to the infrared sensor, a temperature sensor thermally coupled to the cold junction, and electronics coupled to the infrared sensor and the temperature sensor, the electronics determining a patient's temperature in response to outputs from the infrared sensor and the temperature sensor. The kit further includes a first replaceable probe tip defining a first form factor that is specially adapted to accept a first disposable probe cover type, and a second replaceable probe tip defining a second form factor different from the first form factor. The second form factor is specially adapted to accept a second disposable probe cover type. Either of the first or second probe tips can be interchangeably coupled to the tip mounting structure and the infrared sensor.
In accordance with a further aspect provided by the present invention, the sensing system includes a base unit and a measuring unit. The measuring unit preferably provides a self-contained, removable, replaceable temperature sensing probe module. The base unit can, for example, support the measuring unit by providing a temperature display, batteries, a receptacle for storing the measuring unit when not in use, and/or a dispenser for dispensing disposable probe covers. The measuring unit can accept and hold disposable foam probe covers during measurements.
In one example, the sensing probe module measures the quantity of infrared (heat) energy coming from the eardrum, and delivers the measurement to a separate base unit. The base unit develops and displays a temperature indication based on the measurement.
In one example, the base unit includes a dispensing arrangement that dispenses removable probe covers. These probe covers are placed onto the measuring unit probe end before taking a temperature to prevent cross-contamination and for other reasons. The measuring unit probe end may include an ejection mechanism that automatically strips off the probe cover after use. In accordance with a further feature provided by the invention, the measuring unit may sense (e.g., magnetically) the position of the ejection mechanism to determine whether a disposable probe cover is in place and/or whether the probe end has been inserted into the outer ear. By sensing ejection mechanism position, the system can, for example, remind the clinician to put on a new probe cover and/or to prevent taking a temperature before the unit has been properly positioned in the ear.
The electronic signal interface between the module and other system components is digital in the preferred embodiment--improving noise performance and associated accuracy and repeatability and allowing non-shielded cabling such as, for example, a conventional telephone handset cord to be used to connect the display and measuring units. In one example system, all analog signal processing components are contained within the sensing module--with all interfaces to and from the sensing module being purely digital.
In one example, the sensing module provides independent, separately measured thermistor and thermopile digital outputs neither of which is used to "compensate" or otherwise affect the other in any way. These outputs can be digitized by an analog-to-digital converter, and provided to the base unit. The base unit may further process the information to generate an accurate, repeatable temperature reading of the patient's core body temperature.
The following is a non-exhaustive list of additional features and advantages provided by preferred embodiment temperature measuring system in accordance with this invention: